1. Field of the Invention
The present invention relates generally to a liquid crystal display device, and more particularly to a liquid crystal display device having such a structure that a pixel electrode and a common electrode are provided on one of substrates that constitute a liquid crystal display panel.
2. Description of the Related Art
In recent years, flat-panel display devices, which replace CRT displays, have vigorously been developed, and liquid crystal display device, above all, have attracted attention because of advantages of light weight, small thickness and low power consumption. In particular, in an active matrix liquid crystal display device in which a switching element is provided in each of pixels, attention has been paid to the structure which makes use of a transverse electric field (including a fringe electric field) of an IPS (In-Plane Switching) mode or an FFS (Fringe Field Switching) mode (see, for instance, Jpn. Pat. Appln. KOKAI Publication No. 2005-107535 and Jpn. Pat. Appln. KOKAI Publication No. 2006-139295).
The liquid crystal display device of the IPS mode or FFS mode includes a pixel electrode and a common electrode which are formed on an array substrate, and liquid crystal molecules are switched by a transverse electric field that is substantially parallel to the major surface of the array substrate. In addition, polarizer plates, which are disposed such that their axes of polarization intersect at right angles, are disposed on the outer surfaces of the array substrate and the counter-substrate. By this disposition of the polarizer plates, a black screen is displayed, for example, at a time of non-application of voltage. With the application of a voltage corresponding to a video signal to the pixel electrode, the light transmittance (modulation ratio) gradually increases and a white screen is displayed. In this liquid crystal display device, the liquid crystal molecules rotate in a plane that is substantially parallel to the major surface of the substrate. Thus, since the polarization state is not greatly affected by the direction of incidence of transmissive light, there is the feature that the viewing angle dependency is low and a wide viewing angle characteristic is obtained.
In this liquid crystal display device that makes use of the transverse electric field, the counter-substrate is in an electrically floating state. Thus, there is no escape path for static electricity that has come from the counter-electrode side, and the static electricity that is charged in the counter-electrode stays there and may disturb the transverse electric field that is produced on the array substrate side (or a vertical electric field may be produced). Owing to such abnormality in the transverse electric field, a display defect may be caused.